TimePure.hs

{-# LANGUAGE CPP #-}
{-
	Copyright (C) 2010 Dr. Alistair Ward

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
-}
{- |
 [@AUTHOR@]	Dr. Alistair Ward

 [@DESCRIPTION@]	Determines the CPU-time, required to evaluate the specified pure expression.

 [@CAVEAT@]

	The function used to force evaluation of the pure expression 'rnf',
	& the type-class which the polymorphic data must implement 'NFData',
	have been relocated from module "Control.Parallel.Strategies" to "Control.DeepSeq".
-}

module ToolShed.TimePure (
-- * Functions
	getCPUSeconds,
	printCPUSeconds
) where

import qualified	System.CPUTime
import qualified	System.IO

#ifdef HAVE_DEEPSEQ
import			Control.DeepSeq(NFData, deepseq)
#else
import			Control.Parallel(pseq)
import			Control.Parallel.Strategies(NFData, rnf)
#endif

{- |
	* Time the specified pure expression.

	* CAVEAT: as a side-effect, the expression is /deep/ evaluated.
-}
getCPUSeconds :: NFData expression
	=> expression			-- ^ Arbitrary polymorphic expression.
	-> IO (Double, expression)	-- ^ The original expression, tagged with the CPU-seconds taken.
getCPUSeconds expression	= do
	start	<- System.CPUTime.getCPUTime
	end	<-
#ifdef HAVE_DEEPSEQ
		expression `deepseq`
#else
		rnf expression `pseq`
#endif
			System.CPUTime.getCPUTime

	return {-to IO-monad-} (fromInteger (end - start) / 1e12 {-convert from pico-seconds-}, expression)

{- |
	* Print the time required by the specified pure expression.

	* CAVEAT: as a side-effect, the expression is /deep/ evaluated.
-}
printCPUSeconds :: NFData expression => expression -> IO expression
printCPUSeconds expression	= do
	(cpuSeconds, result)	<- getCPUSeconds expression

	System.IO.hPutStrLn System.IO.stderr $ "CPU-seconds=" ++ show cpuSeconds

	return {-to IO-monad-} result